1. Field of the Invention
The present invention relates to electric motor brakes, and more particularly pertains to the circuitry and apparatus necessary to implement such a device. Due to the dangers involved in the use of electric motors, and their inherent rotation inertia, it has long been desired to find a practical way to stop the rotation of the motor when the off switch is activated. The inherent danger comes from the devices the motors are attached to and not from the motors themselves. For example, many such motors are used to drive saws and other rotary cutting tools. The delay between the device being switched off and the blade actually stopping has led to many injuries and is a major safety problem in machine shops and home workshops throughout the United States and the world. This has led to the use of many different types of braking mechanisms over the years. These mechanisms are both electrical and mechanical in nature and involve a variety of approaches. These mechanisms have included the use of a physical brake on the motor shaft, and the use of a dynamic braking action in the motor winding. The applicant's invention involves the use of the dynamic braking action mentioned above, but in a novel and improved fashion. In order to make the device more versatile and therefore give it a wider range of application, applicant has designed the circuitry in such a way that the device may be adjusted to the particular device to achieve the maximum effect. The attendant benefit to the end user is that the device will have the optimum amount of braking for the particular circumstances and yet will still adaptable, if needed, to a change in the working environment.
2. Description of the Prior Art
Various types of electric motor brakes are known in the prior art. A typical example of such an electric motor brake is to be found in U.S. Pat. No. 4,334,181 which issued to Dale W. Schroeder on June 8, 1982, and discloses the use of logic circuits to control the operation of a motor brake. U.S. Pat. No. 4,514,677 which issued to George A. Kaufmann, III et al on Apr. 30, 1985, discloses the use of a timing circuit which operates in two stages and is set at a predetermined level and is not adjustable. U.S. Pat. No. 4,547,692 which issued to Carl P. Spaulding on Oct. 15, 1985, discloses a positional control circuit which has as one of its functions, the ability to brake a motor. U.S. Pat. No. 4,5560,913 which issued to Young K. Min on Dec. 24, 1985, discloses the use of sparkless contacts in a relay operated braking circuit to prolong the life of the relays. U.S. Pat. No. 4,612,490 which issued to Ulrich Kagi on Sept. 16, 1986, discloses the use of a fixed timer circuit and the use of a brake on three phase motors.
While the above mentioned devices are suited for their intended usage, none of these devices discloses the operative features of applicant's invention. Specifically, none of the prior art patents either alone or in concert show the use of a simple electronic circuit to control the braking of an electric motor and furthermore none of the prior art shows the use of a separate mechanism with an adjustable timing circuit which can be retrofitted to almost any electric motor driven device. Inasmuch as the art is relatively crowded with respect to these various types of electric motor brakes, it can be appreciated that there is a continuing need for and interest in improvements to such electric motor brakes, and in this respect, the present invention addresses this need and interest.